1. Field of the Invention
The present invention relates to apparatus for locating a cutting bit on a rotary drum used to cut earth, rock, pavement and the like and, in particular, to an improved cutting lacing method and cutter bit assembly.
2. Background
This invention is directed to locating a plurality of offset points with reference to a peripheral surface or portions of a peripheral surface. Although the invention is to such locating it is believed easier to understand with reference to cutter bits for rotating drums of a coal mining machine for which the invention was initially developed. The methods and apparatus apply to positioning cutter bits on chains for trenchers as well. Inasmuch as the principles of this invention in locating bit points (i.e., the points of the bits) applied to rotary cutting drums, the prior methods and apparatus for locating cutter bits on a rotary drum are discussed for the sake of simplicity in understanding the invention. Diameters and lengths of a cutter drum section vary so that, while the procedures discussed are the same, the tools and aids utilized will vary to compensate for the variations in drum diameter. It is also to be noted that a drum section carries various bit blocks at various locations which receive the bits, and pedestals upon which the bit blocks are mounted. The geometry of the bit blocks and bits is known and, for a specific combination, fixed. Accordingly, such bits and drums are described herein as the presently preferred embodiment of the invention.
In materials mining and in other fields in which a large volume of hard materials must be cut, it is typical to employ an apparatus which includes a vertically moveable horizontal axis cutting drum having cutting bits attached thereto. By virtue of the engagement of the cutting bits which are mounted on the rotating cutting drum with the surface to be cut, material is removed from such surface for further processing.
Due to the substantial forces generated during the cutting operations, the cutting bits must be securely mounted on the cutting drums, but must also be readily removable for replacement. In one prior art form of cutting bit holding apparatus, a cutting bit having an elongated cylindrical shank and a hard cutting tip at one end is retained in a cutter bit holder block which is usually welded directly to the cutting drum or a drum pedestal. A shank receiving bore in the bit holder block is adapted for receiving the shank of the cutting bit therethrough.
Cutter drums vary in design for various mining machines including drums manufactured by a specific manufacturer. As is known, a cutting drum may consist of elongated drum sections, end sections and ring sections between the drum and end sections. The drum, end, and ring segments form a cutter head with various cutter head designs being utilized. Regardless of the design of a cutter head or cutting chain, it is necessary that the cutter head or chain cut its own clearance. That is, the bits on the cutter head cut and break the coal, rock or earth such that the cutter head can be moved forward into a coal seam. In this regard, it is to be noted that coal is a fragile material and that the path of movement of a cutter bit through a coal seam to cause coal breakage is an important aspect of proper lacing of the cutting bits on a drum or cutter chain. Also, each section of a cutter head must carry cutter bits to cut its own clearance. A cutter head which cannot cut clearance for itself is not an acceptable mining machine.
In the mining of coal, it is accepted practice to arrange cutter bits on a traveling or rotating member, such as a cutter chain or a rotating drum, such that the cutting edges or tips of the cutter bits travel through separate paths in the coal seam to be mined. There are various factors regarding the cutting of coal seams which are evaluated by various manufacturers of mining machinery in locating cutter bits on a rotating member including, but not limited to, the hardness and abrasiveness of the material being excavated. The locating of the cutter edges or cutting tip points of a cutter bit is referred to as the xe2x80x9clacingxe2x80x9d of a cutter chain or drum and varies among various machinery manufacturers; however, all machinery manufacturers want as accurate locating of the cutter edge or tip point as is possible under the various manufacturing processes.
In the mining and construction industry, the accuracy in connecting a bit holder block to a drum is critical in achieving the designed lacing for the drum. The contact of the conical tip of a cutter bit and the earth strata enhances the rotation of the cutting tool during the road planing operation. The conical tip that actually impinges and rubs against the surface of the earth strata together with the angle of attack enhances or reduces the rotation of the cutting tool. For instance, an increase in the distance that the contact is away from the central longitudinal axis of the hard insert results in an increase in the extent to which such contact encourages rotation of the cutting tool. The angle of attack for cutter bits is designed to optimize rotation of the cutter bit, hence any variation from the designed angle of attack results in a change in the designed rotation characteristics of the cutter bits. Reduced rotation of the cutting tool causes the cutting tool bit to become unevenly worn on one side, for instance, and the cutting bit quickly becomes damaged and inoperative. Such bit holder blocks on rotary drums must be removed and attached back onto the drum. It is well-known in the industry that the accurate lacing of the cutter bits onto a drum is important to the performance of the mining/construction drum. Therefore, the cutter tips must be accurately welded onto the cutting drum or chain. As will be appreciated, such failures of cutter bits are quite costly because the cutting apparatus must be removed from service in order that the remaining portion of the cutter bit can be removed away from the cutting drum and a replacement cutter bit attached.
The typical road milling drum of the past comprises a generally cylindrical drum with a plurality of road milling bit-block assemblies attached to a pedestal or directly to the surface of the drum. More specifically, the holder block, which rotatably holds the bit, is welded to the pedestal or surface of the drum.
In the construction industry for road milling it is essential that that each bit impinges on the road substrate at an exclusive discrete point so that the points of impact span the length of the drum. Typical impact point spacing for road milling has been about 0.625 inches.
In the prior art, methods of locating cutter bit blocks to mining and construction drums have included automated systems that use programmed machines for positioning and welding the blocks in their proper position. U.S. Pat. Nos. 4,897,904 and 4,947,535 disclose automated equipment that places and fixes the tip point with respect to a rotatable drum. The tip point is held in its programmed position at a preselected position by an automated arm having a gripper for grasping the cutter bit holder block. The holder block is welded onto the preselected position. Such automated lacing equipment is expensive and requires skilled technicians to ensure proper programming for the lacing and maintenance of the manufacturing equipment.
When bit holder block location pins were forged perpendicular to the forge parting lines, they were consistent and located the blocks very accurately. For instance, Kennametal"" C10AMC block in the Kennametal Road Planing catalogue, catalogue number BO1-1(12)D1, illustrates a block with perpendicular cylindrical pins which effectively positioned a block on the drum. Also see the prior art perpendicular locating pins in U.S. Pat. No. 5,842,747.
A different method to manufacture (forge) bit holder blocks has been developed recently. This new method of forging produces blocks having the block shape shown in FIG. 1 at 10 and marketed in Kennametal"" 2001 xe2x80x9cRoad Planing Soil Stabilization and Reclamation Toolsxe2x80x9d catalogue, Kennametal Inc., Latrobe Pa., the C10LG block (SAP #: 1012345). The C10LG block is formed by forging the block from steel blanks and stamping out the block shape with reciprocating upper and lower rams. A parting line 23 is formed where the upper and lower rams come together during stamping. The steel is compressed along a reciprocating axis perpendicular to the parting line by the rams. As is well known in the industry, during one-dimensional pressing and stamping processes, it is not possible to form/manufacture a surface oriented at an angle greater than ninety degrees (see dash line perpendicular to parting line 23) with respect to the parting line. Cylindrical pin locator protrusions, therefore, can only be formed projecting from block surfaces perpendicular to the axis of reciprocation of the rams. The cylindrical sidewall of the pins are oriented parallel to the axis of reciprocation of the stamping rams. For instance the cylindrical locator pins on the C10AMC block (SAP 1012285) in the xe2x80x9cRoad Planing Soil Stabilization and Reclamation Toolsxe2x80x9d catalogue, Kennametal Inc., Latrobe Pa., show a horizontal parting line and cylindrical locator pins oriented perpendicular to the horizontal parting line. As seen in FIG. 1, the block cannot be formed with locator protrusions 20 in the shape of cylindrical pins. The bottom surface of the block is not perpendicular to the axis of reciprocation of the rams. As can be seen in FIG. 1, the locator protrusions 20 are not cylindrical. The cylindrical locator protrusion must be truncated along surface 21 because a cylindrical surface cannot be formed perpendicular to the bottom surface of the block. Surface 21 as seen in FIG. 1, at best can only be oriented parallel to the axis of reciprocation of the rams.
The locating protrusion in FIG. 1 changed from a cylindrical shape, as on the C10AMC block, to an irregular shape. The irregular shape still locates the C10LG block, but no longer as accurately as the perpendicular cylindrical shape did. The blocks with the irregular shaped locating protrusion would be susceptible to shift up to {fraction (1/16)}xe2x80x3 (inch) or more while welding the base of the block to the drum. The {fraction (1/16)}xe2x80x3 (inch) shift at the base of the block, it should be recognized, results in an exaggerated shift at the tip point of the cutter bit. Additionally, this inaccuracy and fit play caused by the irregular shape of the locator protrusion results in some blocks being skewed. A slight misalignment at the base of a cutter bit result in a significant shift in the position of the cutter tip point at its very end. A corresponding cutter tip point misalignment of about as much as xe2x85x9xe2x80x3 or more occurs at the cutter tip point of some block systems whenever the base is mislocated just {fraction (1/16)}xe2x80x3. In addition, the block can be skewed about 4 degrees in either direction out of alignment from its designed position. The skew in the orientation of the block can cause premature wear.
Such inaccuracies in positioning the new forge method blocks on drums causes the cutter tip point to miss the discrete point it was designed to cut by xe2x85x9xe2x80x3 inch. Thus, for instance, in the drum lacing example given above of a uniform 0.625 inch spacing, the cutter bit might cut xc2xd inches away from the adjacent previous tip cut and next succeeding tip will accordingly cut xc2xe inches from that cut. The tip that is continually undercutting its fair portion xc2xd inch as the drum operates often does not make sufficient contact with enough substrate to properly rotate, and the cutter tip that is continually cutting a larger share xc2xeinch of substrate becomes worn quickest and is more prone to failure than the other tips due to increased fatigue. If two such adjacent blocks are misaligned toward each other, the spacing might be xe2x85x9cxe2x80x3 (0.625xe2x88x92xe2x85x9xe2x80x3xe2x88x92xe2x85x9xe2x80x3), or if two adjacent blocks are aligned apart from each other, the spacing therebetween would be xe2x85x9exe2x80x3 (0.625+xe2x85x9+xe2x85x9xe2x80x3), perpetuating such problems discussed immediately above to a greater degree. It is preferred in the industry that each tip along the length of the drum is evenly spaced so that all the tips wear and fail at a uniform rate.
Such 0.625 inch spacing is satisfactory for removing road surfaces in some instances. It is, however, on occasion necessary to design a road milling machine that provides for 0.200 inch spacing to make the texture of the road surface less coarse. Such a smooth texture may be required when resurfacing is not being performed, but the road is being milled to smooth out traffic ruts. A coarse textured surface can be irritating to the driver as a vehicle travels over a coarse cut because of the vibrations and high noise level. For such close spacing used to achieve a smooth textured roadway, it is even more critical to have a method for affixing the cutter bit assemblies to the drum/chain accurately without the need for fixturing.
The subject invention is directed toward an improved bit holder block locating design and method and which overcomes, among others, the above-described problems with prior art bit holder blocks and provides a bit holder block which is much less prone to such failures and the concomitant apparatus downtimes, while being capable of being manufactured at similar costs thereto.
The subject invention overcomes the problems in the prior art in a cutting tool assembly having a holder block mounting scheme which effectively and accurately positions the cutting tip point at its designed angle of attack.
In accordance with the present invention, there is provided a bit holder block assembly for attachment of a cutting bit to a cutting drum. The cutter bit block assembly includes a separate mounting plate that is positioned between the bit holder block and drum/pedestal for accurately aligning the bit holder block to the drum/pedestal. Once the bit holder block is aligned into position by the plate as designed, the bit holder block is welded to the drum/pedestal.
In one embodiment, an adaptable plate is designed with circular openings at one end and an elongated oval opening at the other end so that locating protrusions with different relative spacing therebetween may be used with the plate. The mounting plate with its oval opening can accommodate block designs with locating protrusions having different spacing.
In another embodiment, the alignment members are hexagonal and cooperate with hexagonal holes on the base/pedestal for fixing the holding block in position.
Accordingly, the present invention provides solutions to the aforementioned problems present with prior art cutting bit holders. These and other details, objects and advantages of the invention will become apparent as the following description of the present preferred embodiment thereof proceeds.